docs: def convert(self, destination_units):
          """Convert units.
  
          Parameters
          ----------
          destination_units : string (optional)
              Units to convert into.
          """
          if not wt_units.is_valid_conversion(self.units, destination_units):
              kind = wt_units.kind(self.units)
              valid = list(wt_units.dicts[kind].keys())
              raise wt_exceptions.UnitsError(valid, destination_units)
          if self.units is None:
              return
  
          def f(dataset, s, destination_units):
              dataset[s] = wt_units.converter(dataset[s], dataset.units, destination_units)
  
          self.chunkwise(f, destination_units=destination_units)
          self.units = destination_units